Compound Interest Calculator
Watch contributions compound over time with an interactive growth curve
Final balance after 20 years
$145,180
Total contributions
$58,000
Total interest earned
$87,180
Growth Over Time
Year-by-Year Breakdown
| Year | Contributions | Interest | Balance |
|---|---|---|---|
| 1 | $12,400 | $816 | $13,216 |
| 2 | $14,800 | $1,864 | $16,664 |
| 3 | $17,200 | $3,162 | $20,362 |
| 4 | $19,600 | $4,727 | $24,327 |
| 5 | $22,000 | $6,578 | $28,578 |
| 6 | $24,400 | $8,737 | $33,137 |
| 7 | $26,800 | $11,226 | $38,026 |
| 8 | $29,200 | $14,068 | $43,268 |
| 9 | $31,600 | $17,288 | $48,888 |
| 10 | $34,000 | $20,916 | $54,916 |
| 11 | $36,400 | $24,978 | $61,378 |
| 12 | $38,800 | $29,508 | $68,308 |
| 13 | $41,200 | $34,539 | $75,739 |
| 14 | $43,600 | $40,108 | $83,708 |
| 15 | $46,000 | $46,252 | $92,252 |
| 16 | $48,400 | $53,014 | $101,414 |
| 17 | $50,800 | $60,438 | $111,238 |
| 18 | $53,200 | $68,572 | $121,772 |
| 19 | $55,600 | $77,468 | $133,068 |
| 20 | $58,000 | $87,180 | $145,180 |
How it works
This calculator runs a month-by-month simulation: each monthly contribution is added to the balance, and interest is applied at your chosen compounding frequency (the annual rate divided by the number of compounding periods). The chart shows your total balance in indigo and your cumulative contributions in gray -- the gap between them is the interest your money earned. All calculations happen entirely in your browser. Results are estimates and do not account for taxes, fees, or variable returns; this is not financial advice.
Free Compound Interest Calculator
This free compound interest calculator shows you exactly how your money can grow over time. Enter your starting balance, monthly contribution, interest rate, and time horizon, and instantly see your projected final balance, how much of it came from your own deposits, and how much was pure interest. An interactive growth chart and a year-by-year breakdown table make it easy to see the compounding "snowball" in action.
What Is Compound Interest?
Compound interest is interest calculated on both your original principal and on all the interest that has already been added to it. With simple interest, a $10,000 deposit at 7% earns the same $700 every year. With compound interest, that $700 is added to your balance, so the next year you earn 7% on $10,700, then on $11,449, and so on. Over long periods this difference becomes enormous, which is why compound interest is often called the most powerful force in personal finance.
The Compound Interest Formula Explained
The standard compound interest formula is A = P(1 + r/n)^(nt). In plain language:
- A is the final amount you end up with.
- P is the principal — the amount you start with.
- r is the annual interest rate written as a decimal (7% becomes 0.07).
- n is how many times interest compounds per year (12 for monthly, 4 for quarterly, 1 for annually).
- t is the number of years.
So the formula simply says: divide the yearly rate into smaller chunks, apply one chunk each compounding period, and repeat for every period across all your years. When you also make regular contributions, each deposit starts its own compounding journey from the month it is added. This calculator handles that automatically with a month-by-month simulation, so the results reflect exactly when your money starts earning.
How to Use This Calculator
Start with your current savings as the initial principal, then add a realistic monthly contribution. For the interest rate, savings accounts might earn 4–5%, while long-term stock market returns have historically averaged around 7–10% before inflation. Drag the years slider to compare time horizons — extending from 20 to 30 years often more than doubles the interest earned, which shows why starting early matters more than starting big.
Why Compounding Frequency Matters
Interest that compounds monthly grows slightly faster than interest compounding quarterly or annually, because earnings get added to the base more often. Use the frequency selector to compare scenarios and match how your actual account compounds.
A Note on Accuracy
These results are estimates based on a constant rate of return. Real investments fluctuate, and the calculator does not account for taxes, fees, or inflation. Use it for planning and comparison — it is not financial advice.
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